1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a rotatable inverter for inverting a DC power source into an AC power source.
2. Description of the Prior Art
Generally, an inverter is an apparatus for inverting a DC power source into an AC power source. A Conventional relay or a semiconductor device has been provided in the inverter. Recently, the semiconductor device such as a thyristor is most commonly employed.
FIG. 1 is a circuit diagram of a conventional inverter employing the semiconductor device. As shown in FIG. 1, the circuit of the conventional inverter employing the semiconductor device is comprised of a DC power source, a trigger circuit 10, a plurality of thyristors th1 and th2, a condenser C1 and a transformer 20. The plurality of thyristors th1 and th2 are switched on/off by a switching operation of the trigger circuit 10, and a current in the primary coil 21 of the transformer 20 is thus outputted in turn, thereby generating the AC power source having a desired voltage in a secondary coil 22.
The inverter employing the semiconductor device is connected to household electric appliances such as a microwave oven so as to supply an AC power source to the household electric appliances. Therefore, these household electric appliances can be used even in the open-air or on a ship, in an aircraft or any other vehicles where the AC power source is not available. Here, the microwave oven is an apparatus for cooking food by using microwaves. The microwave oven is provided with a high voltage transformer and a magnetron. The high voltage transformer serves to step up the AC power source supplied from the inverter to a high voltage of about 2,000 V. The magnetron is driven by the high voltage and radiates microwaves of a desired frequency. The microwaves vibrate molecules of moisture contained within the food. Therefore, the food is cooked by the frictional heat generated by the vibration of the moisture molecules.
However, in this type of AC/DC microwave oven provided with the inverter employing the semiconductor device, there is a problem. That is, since it is necessary to provide a plurality of expensive semiconductor devices for the inverter in order to output a desired high voltage for the magnetron, the manufacturing cost is increased.
In the above conventional AC/DC microwave oven, there is another problem that the life span of a battery which supplies the DC power source is short, since the attrition rate of the current by the semiconductor device is very high.
In the above conventional AC/DC microwave oven, there is another problem that, since the semiconductor device generates excessive heat, energy loss by the heat is increased.
In the above conventional AC/DC microwave oven, there is a further problem that, since the size of the cooling fins is increased to cool the semiconductor device, the size of the microwave oven has also to be increased.